Method for cooling gaseous media by interchange of heat with cooling gases



Dec. 30, 1947.

D. A. RHoADEs 2,433,397

METHOD FOB. COOLING GASEOUS MEDIA BY INTERCHANGE OF HEAT WITH COOLING GASES Original Filed March 2l, 1945 5 Sheets-Sheet 1 2,433,397 INTERCHANGE 5 Sheets-Sheet 2 m Y S .B A sus ED G DEN A L oso UO Hm C RSH .m H A W G T Dm m @H O F CO R O F D O H .m 7M 4 9 l De-c. 30,

Original Filed March 2l, 1945 Dec. 30, 1947. D. A. RHoADl-:s

lMETHOD FOR COOLING GASEOUS MEDIA yBY INTERCHANGE OF HEAT WITH COOLING GASES Original Filed March 21, 1945 3 Sheets-Sheet 5 INVENTOR. DONALD A. RHOADES Patented Dec. 3f),V 1947 METHOD FOR COOLING GASEOUS MEDIA BY INTERCHANGE OF HEAT WITH COOL- ING GASES Donald A. Rhoades, Palo Alto, Calif., assigner to The Permanente Metals Corporation,

Oakland,

Calif., a corporation of Delaware Original application March 21, 1945, Serial No.

585,884. Divided and this application February 1, 1946, Serial No. 644,958

6 Claims.

1 The present invention relates generally to a method for cooling gaseous media by interchange of heat with cooling gases, and more particularly for condensingvapors, such as metallic vapors which are mixed with gases that have a tendency to react chemically with the said vapors. However the invention will be described, for purposes of illustration, with particular reference to the manufacture of magnesium fromV magnesia or magnesia-containing ores while using a carbonaceous material as the reducing agent.

In the thermal reduction of magnesium oxide with carbon the reaction proceeds according to y the equation MgO-l-CMg-l-CO with production of a mixture-of magnesium vapor and carbon,`

monoxide. At a sufficiently high temperature the reversion of the reaction from right to leit is eiciently repressed, but if the reaction products are allowed to cool gradually the reverse reaction progresses so rapidly that the starting materials MgO and C are reformed substantially completely and no material amount of magnesium is recovered.

It is now well known that the reversion of the reaction can be minimized by keeping the mixture of magnesium vapor and carbon monoxide up to the point at which it leaves the furnace at such a high temperature that the reaction proceeds practically to the right, and then suddenly cooling (shock-chilling) the mixture at this veryV point, by the injection of iinejets of a non-oxidizing gas, down to a temperature at which under the dilution conditions existing magnesium and carbon monoxide are stable in the presence of each other. the solidiiication point of metallic magnesium, 4the metal is condensed in this way in the form of a iinely divided dust. Usually shock-chilling is effected by introducing into the escaping mixture of highly heated reduction products a cooled gas, which is inert or substantially inert to magnesium, such as hydrogen or a noble gas, particularly helium, or in industrial hydrocarbon, or natural mixtures of hydrocarbons such as natural gas.

As large quantities of the chilling gas are re quired in commercial operations of any appreciable scale, with coolants other than natural gas, it is unavoidable to returnthe coolant in cycles, and this can not be done without removal of carbon monoxide before recirculation. However, it is already known that it is not necessary to reclaim the entire volume of gas employed for chilling, but suffices to remove an amount of carbon monoxide corresponding to the increment due to Since that temperature lies below had previously l eliminating or materially reducing the CO con- CO formation in the reduction stage. For that purpose it has been proposed to divide the gas mixture left behind after separation from the powdery condensate, into two portions, of which a smaller one is detached for reuse in an unchanged condition, whereas the other portion is subjected to a treatment capable of reducing the carbon monoxide content therein; eventually these two fractions are united to lead back into l the circuit the gas mixture thus obtained (of. U. S. Patent No. 2,200,772).

It is a particular object of the invention to provide a method in which a portion of the chilling gas used is recirculated in a cooled but otherwise unchanged condition, and a quantity of fresh gas or recirculated gas substantially freed from carbon monoxide, which is referred to as make-up gas in the following, is added to the vapor-gas mixture to be chilled at a point and in a manner to obtain the greatest shock-chilling efficiency.

Other objects and advantages of the invention will become apparent from the following description taken in connection with the accompanying drawings.

To accomplish these objects the invention essentially contemplates that the recirculated gas and the make-up gas are maintained separately and separately intermingled with the gas vapor mixture to be chilled while introducing the make-up gas into the flow of the hot reduction products to be chilled at a zone in advance of the introduction of the gas that is recirculated in a cooled but otherwise unchanged condition. The recirculated gas then enters the flow to supply the balance of the required volume and supplement the cooling effect of the make-up gas.

Natural gas which is available in large quantities and inexpensive enough to be subsequently burned as a fuel, is most attractive for use as a chilling agent in the service of the carbothermic method of producing magnesium. For these reasons the present method, too, is particularly 4adaited to be applied in connection with chilling the vapor-gas'mixture escaping from the reduction furnace by means of natural gas, of which a portion is reused in a cooled but otherwise unchanged condition with the addition o f fresh gas, whereas the other portion passes off to be led into a fuel system; In case of using gases other than natural gas as' coolants, the portion introduced as fresh gas in the case of natural gas has rto consist of recirculated coolant which been subjected to a treatment for :.tion;.of the device :the l rightY har1d-fend,= and '-.tionof the devicef'shownfin llg;j 1,theouter -part thereof .being aremovedrto disclese tween the hottest vapors and.thefcoldestgasunder highest pressure. The rate of back reactionf-is evidently greatest at elevated temperatures which are only slightly lower than the equilibrium temperatures for the operating conditions of the particular vpartial pressures involved. Therefore the lower the percentagexof CO `*inthe coolant initially introduced andthe morerapid the initial .cooling rate, themore eiiectivet-he shock-chilling operation. :Whether the `make-up :gas consists of vfresh gas orrof appropriatelyreclaimed-reeir fculated gas, 'all-in. allthis .arrangement results `in asaving :in-.volume :as :fwell as Iin; .pressure and cooling of the total:quantitymffgas necessary to gain` the Vdesired'end.

No matter what gas is'used, fitrfmustenterzthe i chilling cone .atz aptemperature;V sufficiently below theL-fnal shock-chilling- :temperature .that ais ap- :proximately:at;200".C.,` .toleiectya coolingfwithout resorting to circulating .impractical quantities of .'gas. The :proportions offchillingfgas circulated fand-makeup gas introduced-on .thev one-jmmd,- and :the f entering temperatures on the ;othe r, .hav e lto ,'beI balanced against:eachothertoarriveat favor- -able 'economical `vworkingconditions. The pressure at which the make-up gas andy hegrecirtculated; gas,. respectively,; are .elevated 11s ikezvise a function. ofeconomics.toachievefrapidrmixing'in .a@limited.distancegrom-the:outletrportawithout resorting to excessive horsepower forcompresf1.

sion. It is obvious that*:thi s,.ftoo.tiesfin-with jthe quantities of: gas to be;r circulatedf-whichson 'their --partare .a lfunctionV of fthe temperatureapparatus '.which may -be usedgac Coming-to `the invention for,I carrying out the-'process de- .scribed is illustrated:.by= way ofrexample .inathe Aaccompanying (drawings.

Fig.' l isf-fa longitudinal .sectional view :taken through a chilling :sdevicewhich l. embodies the present invention.

Fig: 2 is' an enlarged fragmentary.detailfinvsection of a part of the inner end ofthe; devicev shown in Fig. 1.

' Fig. 4jis a fragmentary isometricview D rangement-pf parts-,hidden Fthereby.

I he apparatus shown, y,comprises an -rinnelhell I in thejshape.otsaztruncateducone whic ,leconnected atits: innerxend, thatcis trie-.er1 dginr juxtaposition tothe outletopening-in the furnaceswall. '-.with ,a perforated or slotted'frllsto conica aber II whichserves aszaznoletplallef bernd- -mis'sion of the'chilling y :manner lof nozzlesy in 'directing-fthegas. t0 .the i11- fterioru of 'the rusto-conic'ally .shapedvmember vI ll. ``:While `the nozzleopeningsherein shown-.are :inthe gas, its.l slots. actingdnithe Showniinliiel lilas-viewed :frein 1 ..-shown et l 15in. Figs. 11. land .2- ;enters. the manifold milled 'slotsappear'to-be entirely adequate for the introduction'oftherecirculated gases at relatively lower pressures'which latter may contain a small @amount oflsolidparticles owing to imperfect or .damaged-.dust iiilters. It appears that dust that -collects `at-the edges of the openings tends to break away and free itself more readily from the ,.longedges of,. the,slots than it does from circular openings.

The members IU and I I are surrounded by a .frustconical outer shell member I2 spaced from the member I0 to forma channel or passage of conicalcontour through which :ges may be deliveredvto the nozzleplate II. The members I0, II, and I2 are connected together by means presently to be described to form a .unitwhich is .insertable in asuitable recess in thewall I 3 of the furnace so that the inner end .of 4the frustoconically shaped ;unitcommunicates `with Vtheinterior of the furnace ,Crucible while theouter end thereof projects. to a point outsidethewall of the furnace where it is connected .with adust collecting chamber .or other .dust. collecting and sepa rating device.

As shown in Figure ltheoutlet-of the wall .I3 vof the furnacecrucible is linedv with anannular yreplaceable insert. I4 of. graphite ,or other material resistant totheerosiveeflects of the-hotle- .duction products vescaping from the furnace. The vfurnace usually has an outer metallic Ashell 5 spacedfrom therucible, and the space .between the shell and thev crucible'is flledwitha heat insulating, materiali whchfmay be lamp black-or other nely divided carbonaceoussubstance. In the present instance an opening for thegreception .ofthe .chilling eenefisdenedthreugh,the furnace .insulating materiely by..a..,d0uble .Walled HustocQIliQ9l mmbr I5 which .isooled .by a liquid coolant suchl as o il for;its own protectionand also for -.the protection of the chilling cone against the furnace heat. A connection ismadebetween the member I5 and the furnace wall5 by meansof a pairof flanges 'I,one carried by the furnace wall, and thepther by the member I5. VThe inner end of thamember .I 5 is spaced` at vs hort distance from the outerwall ofi the furnace andthe space is sealed rby packing 8L of asbestos rope or other material capable of preventing leakage of the finely divided-insulating material to the ,interior of ,the space occuped by the -chilling cone. This Vloose connection between the cone I5 and ythe :furnace crueible permits theerueible to expend -beth radially .and ,vertically Witheet Contacting .er distorting ,theene. Ilneinner end of .the .member .l 5 isslif ientlytlerge lndlenieter tepel'.- .rnit removal and., eplaeement of tnegrephteinsert I4 which may become eroded or otherwise .defective after. lens-centime@ .Service-.due .te Vthe temperature andneture ,Qf thevapQrnhiehraeSes :through it.

...The eoelinsnuld.mastbeintredueedfte.the inte- -ltier .of .the Yxr1l 1nl1ie1- l5 .threneh@annular-.man1- iioldripe :I6 adjacent .toits-enterend-.end cem- .municated 4to itsinner en d through a;plur ality of. longitudinally extending'. pipes, ene of which is The; Yeenling ,fluid I6 threugh; asupplyspipe .I8

Maase? and is conducted through the pipes I1 to the innermost end of the space through which it is circulated, then flows back around the outside of the pipes I 1 and passes out through a discharge pipe I9. The inner ends of the pipes I1 are preferably out at an angle, as illustrated, to cause the cooling fluid delivered through the pipes to sweep the interior of the space to be cooled with a sort of circular motion and thus maintain a constant movement of the coolant against the surfaces as it flows back toward the discharge pipe I9. The outer end of the double walled member I5 is provided with a flange 20. A gas'tight connection between this flange and a manifold housing 2I, which is carried by the outer shell I2 of the chilling cone, is formed by an expansion plate 9 which is in the form of a flexible metal ribbed annulus fastened at both edges by cap screws and suitable gaskets or the like (not shown) for forming a perfect seal. This expansion plate 9 provides suicient flexibility to absorb movement due to expansion and contraction between the member I5 and the enclosed chilling cone. The inner end of the chilling cone assembly is, as will presently appear, also spaced slightly from the crucible to permit movement in all directions resulting from expansion and contraction.

The chilling gas is delivered to the outside 0f the outermost end of the nozzle plate II through the manifold 2l which surrounds the outer shell I2 adjacent to its right hand end and communicates with the space between the shells Il) and I2. To introduce the portions of the recirculated gas and make-up gas separately and at different points in the flow of the gaseous reduction products to be chilled, the supply manifold 2I through which the chilling gas is introduced is divided by an annular wall 22 to form an outer manifold 23 for make-up gas, and an inner manifold 24 for recirculated gas. As shown in Fig. 3 a supply conduit 25 for recirculated gas extends through the outer manifold and communicates with the inner manifold 24, while a supply conduit 23 for make-up gas communicates directly with the outer manifold. The recirculated gas entering through the manifold 24 flows inwardly between the conical shells I0 and I2 in cooling contact with the exterior of shell I0 and then passes through the slots of the nozzle plate II into the interior of the chilling cone where it mingles with the hot furnace products. On the other hand, the make-up gas which enters the manifold 23 is communicated by pipes such as indicated at 21, to the left hand end of the space between the members I0 and I2 and through a wall 28 which forms the inner boundary of the main Portion of this space and which separates the inner portion of the nozzle member II from the outer portion thereof. Thus the make-up gas is supplied to a small annular chamber '29 and escapes through openings in the inner end of the nozzle plate II to mix violently with, and chill, the furnace vapors immediately as they emerge from the crucible at a point in advance of the introduction of the recirculated gas. The inner portion of the chamber 29 is defined by a double walled flange 30 the interior of which provides a casing for the circulation of a cooling fluid and thus protects the entire inner face of the chilling cone from the heat of the furnace. Cooling fluid ls supplied to the protecting flange 30 through a plurality of small pipes 3| which communicate with an annular manifold pipe 32 disposed within an exhaust manifold chamber 33 that is formed by a wall 34 defining the right hand end of the space between 6 the shells I0 and I'2. The cooling fluid is furnished to the supply manifold through a pipe and ows from the manifold through the pipes 3 I which penetrate the wall 34 and also the wall 28 and terminate, as best shown in Fig. 2, adjacent the innermost end of flange 30 where they are preferably cut diagonally to induce a circular or sweeping flow within the flange. This coolant discharges through pipes 36 one of which is shown in the lower part of Fig. 1 and which, as also illustrated in Fig. 4 communicate with the interior of the flange 30 and with the exhaust chamber 33, from which the fluid escapes through a discharge pipe 31. It is an advantage of the arrangement herein shown that the chilling gas enters through what may be likened to a very large conduit so that a lower initial gas pressure will suffice to deliver a large volume of gas and produce a high nozzle velocity at the nozzle plate Il. While the space between the members I0 and I I includ-es the make-up fluid pipes 21 and the cooling gas supply and discharge pipes 3l and 36, all as illustrated in Fig. 4 of the drawings, there still remains an unusually large area for the transmission of recirculated gas to the nozzle. A

In Fig. 4 the relative positions assumed by the pipes 21, 3|, and 36 are indicated and the pipes 3I and 36 are shown as provided with expansion bends 40 which serve to absorb any distortion ref' sulting from variations in temperature. Such a. bend is preferably eliminated from the pipe 21, the inner end of which is loosely fitted in a suitable perforation in the wall 28 so that it is free to move lineally when subjected to temperatures different from that of the parent member. The sliding flt of the pipe 21 where it pierces the wall 28 may permit leakage of a small quantity of make-up gas through this wall, but this leakage is of no consequence because the escaping gas simply enters the area occupied by the recirculated chilling gas.

Fig. 4 also illustrates one of a plurality of spacer plates 4I which may be disposed between the inner and outer shells In to brace and maintain them in their concentric positions. The Spacer plates and pipe occupying this area may be as numerous as required by the functions which they perform and yet leave the space substantially unobstructed for the passage of a very large volume of a chilling gas which serves as a coolant in contact with the inner shell II) and which eventually enters through the nozzles the interior of the cone where it chills the furnace vapors by dlrect contact.

The form of the apparatus herein disclosed permits the use of Scrapers for maintaining the inside surfaces of the conically shaped chilling chamber free of undesirable deposits. Likewise, spray devices may be employed for wetting and rendering inactive pyrophoric materials within the cone prior to its being opened to the atmos phere for inspection and repair. Such Scrapers and spray devices are well known to the art (cf. U. S. Patent No. 2,109,841). Besides their illustration herein is unnecessary to an understanding of the present invention.

The term make-up gas is used in the following claims to include not only fresh gas, but also reclaimed gas which is substantially free from, or low in, carbon monoxide.

This application is a division of my copending application, Serial Number 585,884, filed March 31, 1945.

. Ii-claim; y 1i In tl,1e,-processof,` making;metallicmagne` sium inwhicha mixture -of magnesium `Vapor4 and carbon-*monoxide gasf is chilled suddenly, by intermingling a chilling gas therewith,vfromt a highy temperature at which thefreaction proceeds practically from left to right', to a' low temperature at which reoxidation of the magnesium-formedby the carbon monoxide present is minimized, the steps ofrecirculating some of the chilling gas employed and continuously adding a quantity of make-up gas, the said make-up gas being. introduced intol the ow ofthe vapor-gas mixture to be chilled in a zone precedingthezone of introduction of the recirculated' gas.

2.: In the process of makingmetallic magnesium inwhich a mixture of'rnagnesium vapor and-carbon monoxide gas is chilled suddenly, by inter-` mingling a chilling gas therewith, from a high temperature at. which the reaction MgO-l-CMg-i-CO proceeds practically from left to right, to a low temperature at which reoxidation ofthe magneand separately adding asupply of make-.up gas by introducing thesame tothe flow of-'the vapor-gas mixture tofbe,` chilled` in a zone preceding that where the recirculated gas is added.

3'. In the process of cooling, gaseous media compr-ising magnesium and'carbon monoxide by interchange of heat with cooling gases, that combination of steps which comprises separating a portion of the exhaust chilling gas, recirculating a stream of the separated gas in a cooled but otherwise unchangedcondition into the medium toV be cooled, and separately adding a quantity of make-up gascooled toa lower temperature and elevated at a higher pressurethan is the recir-v culatedgas, by introducing. the said make-up gas into the ow of the mediumv to be cooled in a zone preceding that of the introduction of the recirculated gas'.

4. The process of claim 1, wherein the chilling gas is natural gas.

5. The process of'claimrl, wherein the chilling gas is hydrogen.

6. The process of claim 1, wherein the chilling gas is a noble gas.

DONALDA. RHOADES.

REFERENCES CITED UNITED STATES PATENTS' Name Date Erdmann May 14, 1940 Number 

